2) download ASTER-GDEM relief data for your area from http://gdex.cr.usgs.gov/gdex/ (registration is free). Use options to create zipped data files.
The selected area must have a rectangular shape and coordinates of it's borders must be integer.

3) Create folder \BLX inside of MobileMapper Office \MAP folder (\VectMaps for MMO 2.7 if a map working folder is in MMO 2.7 working folder)

15) Open \MAP\topo3d.ini and write the name of your file in BLX section

[BLX0]
0=file.blx

Note. It is not necessary that the entire grid of heights that covers your map was in one blx file. If the area is too large the creation of such a file can take too much time. You can break the coverage area of the map into several parts created as separate blx files and place them all in a folder

So, if you created several .blx files, then you can add them all here

[BLX0]
0=file1.blx
1=file2.blx
...
N=fileN.blx

16) Run MobileMapperOffice and create map. Relief data will be added automatically and truncated to the rectangle of your map.